1. Field of the Invention
This invention relates to an improved closure mechanism, and more particularly to an improved mechanism for closing a lid, door or the like which prevents the lid from overextending, holds it firmly in a predetermined open position, and controls the rate of closure thereof.
2. Description of the Prior Art
Situations often exist in which a heavy closure object of some sort, such as a lid, a door or the like is required to be retained in at least one fixed open position for some time. In such cases it is also often desired that the lid be easily opened. It is also frequently desirable that the lid close in a controlled manner. This is especially true when the lid closes to a horizontal position--if the lid is heavy, having it fall to a closed position abruptly creates a safety hazard for the person closing it, as well as for bystanders. In addition, having such a heavy object fall precipitously, creates a loud and startling noise. This may be especially undesirable in circumstances where the bystanders may be particularly sensitive to such an occurrence, as will happen in the workplace, for example, or when the falling object is a lid to a casket.
In addition, it is desired that when the lid opens, not only does it do so easily, but also that it only opens to a predetermined position and no further. Thus, it may be undesirable for such a lid to be able to overextend. Particularly if the lid can be rotated past its vertical position, it may fall horizontally open, again causing a hazard. Furthermore such overextension can lead to damage of the supporting structure and perhaps the lid itself.
The problem of controlling the rate of movement of a lid or other heavy object has been addressed in the prior art, particularly in respect to the opening, propping open, and closing of automobile hoods and trunks. However none of the prior art has disclosed the combination of means used in the instant invention to allow easy opening of a lid while preventing overextension thereof, maintaining the lid in a fixed position, and retarding the closing motion of the lid.
Thus for example, U.S. Pat. No. 2,953,810 to Hall describes a door closing device that allows rapid closure of the door to be accomplished by the use of force. Control is achieved through the use of a spring.
U.S. Pat. No. 4,796,871 to Bauer et al. discloses a gas spring with end position dampening. A throttle piston is slideably mounted on the piston rod that is actuated as the piston moves toward the end of the stroke to create a force that opposes the further movement of the piston rod.
U.S. Pat No. 4,178,655 to Little is directed to providing damping at both extremes (the opening and closing of a lid) without retarding the speed of the operation between the two extremes. A spring is used in conjunction with fluid to both provide the force necessary to hold a lid open and to control the rate of movement as it opens and closes.
U.S. Pat. No. 4,323,224 to Freitag et al. involves a gas spring with means for impeding the movement of the piston away from one of the terminal positions. Control is maintained via a valve plate. The piston is maintained in place through the use of two equally pressurized chambers.